The present invention relates generally to metallic glasses and, more specifically, to a method of fabricating metallic glasses into bulk product forms.
Generally, glass is a solid material obtained from a liquid that does not crystallize during cooling. A glass is an amorphous solid, meaning that atoms comprising the material are randomly arranged as opposed to an atomically ordered, crystalline structure. The most common meaning associated with the word glass is the familiar, transparent material commonly used in a myriad applications in everyday life. That glass, formed mostly of silica, is an electrical insulator and non magnetic.
A new class of material, called metallic glasses, was discovered in the 1960s. Unlike conventional metals, metallic glasses have a noncrystalline or amorphous atomic structure. Metals, as a rule, crystallize readily upon cooling. It was discovered that a rapid quench of the liquid metal, in the order of a million degrees Celsius per second, allowed the solid metal to retain its liquid, amorphous state. Metallic glasses possess a number of desirable properties such as very high elastic limit, excellent magnetic behavior, extremely high yield strength and resistance to wear and corrosion. They are useful in many products ranging from motor components to golf clubs.
A significant downside to the more widespread use of metallic glasses is the difficulty in manufacturing them into bulk product forms. Generally, the exceedingly high quench rate of the prior art processing techniques is amenable only to very thin layers of material, of the order of much less than 1 mm. There have been developed only a few alloy compositions that do not require the above described high quench rate and that allow for the direct production of metallic glasses in bulk product forms (greater than 1 to 2 mm thick.) Again, the vast majority of known metallic glass alloy compositions require cooling rates in excess of 103 K/s, so that the maximum material thickness that can be produced in the amorphous state is much smaller than 1 mm. While some investigators have resorted to a powder metallurgy approach, consolidation of atomized powders of these alloys poses a significant technical challenge due to the extremely high strength and low macroscopic ductility of amorphous alloys. These metallic glasses typically crystallize at temperatures below those used in conventional processing practice to outgas and consolidate metal powders, which would destroy the amorphous atomic structure and the unique properties provided by the amorphous atomic structure. Thus, consolidation of amorphous metal powders cannot be accomplished by standard techniques.
The intrinsically poor fracture properties of amorphous metals are also a serious issue. Tensile ductility for amorphous metals is typically near 0%. Thus, widespread use of amorphous metals in fracture-critical structural applications will not occur until the fracture properties are improved and the technical hurdles described above are solved.
A need exists therefore for an improved method of fabricating metallic glasses in bulk product forms as well as improved metallic glass microstructures resulting from the improved method.